I am attempting to build a robot arm. I am having trouble selecting functioning servos. At first I bought a 20 pack of generic 9g servos on eBay. Half arrived pre broken, the other half broke within an hour of use under no load. I assumed I got a bad batch, got a refund, and bought a different brand of similar servos. The exact same thing happened, and I discovered the servos were not strong enough anyway. I then upgraded to the mg995 metal gear servo. These servos worked fine for a day, then three out of the four failed. Upon opening them, I discovered that the metal gears had failed in all three. Under no load. Really. At this point I was getting frustrated, so I bought four mg996r "metal gear" servos. These did not turn easily at all, lots of internal resistance, which unsurprisingly led to all four servos failing in about ten minutes. Upon opening these servos, it turns out that "metal gear" was technically correct, as exactly one of the gears inside was metal. The other gears were plastic made so poorly that they simply did not mesh well, likely causing the friction that caused the failure. So at this point I have no robot arm, lots of useless pieces of plastic, and a headache all for the low cost of 120 dollars. I would like to purchase WORKING servos that can actually function for more than a day. Ideally I would also like to do so without spending the GDP of a small country. Ideally less than ten dollars a servo, with at least 10 kg/cm of torque, though at this point just functioning servos at all is a high bar. Where do I purchase WORKING servos, how much will it likely cost (I need a lot) and how do I tell in the future whether a given servo is a complete scam, because I am sick and tired of this.
There are many cheap clone servos around and it sounds like you've been buying lots of them. I'm sorry but the answer is to buy your servos from a reputable supplier, not Ebay and not China. As you've discovered buying from those sources is just gambling. But they will NOT be as cheap. Using decent materials and having reasonable quality control costs the manufacturers money and they want to recover it.
You might also want to do some calculations and work out what specification of servo you actually need. Since some servos in robot arms are under permanent load holding the weight of the arm components they need to be more powerful than you might at first think. Good luck.
Steve
What kind of price range would I be looking at per standard size servo? I don't need exact, but I am going into this completely blind and I would at least like to know a "reasonable range" for a hobby servo, even if it is a wide range. Also, what suppliers would you recommend?
Servos come in all sorts of shapes and sizes. There isn't really a "standard size servo". As I said before you need to have some idea of what specification you need. As you're the only one with any idea at all of the size, weight, construction etc of your robot arm I can't really help there.
Steve
40 mm standard size 10 kg/cm 180 degree I really don't need specifics if a servo with that specification comes up for 500 dollars is that too high? I am assuming less than ten dollars guaranteed cheap bad servo. If you could just give me a ballpark I would at least have SOMETHING to go on. Literally any range would help me narrow it down here.
I buy most of my servos from Hobbyking. Have a look at https://hobbyking.com/en_us/radio-servos/servos/all-servos.html
In their "standard" servos you should find some 10kg.cm roughly 50-60gm servos. Prices probably around $10-15.
But there are many other suppliers, some specialising in robotics like Robotshop.com and others like Sparkfun.
Steve
Check out servocity MOTION - ServoCity
They have lots of servos and accessories, plus step files for a lot of their servos and accessories. It's very useful since, as previously stated, not all servos have the same dimensions. This way you can either design around your servo, or see if the servo will fit in the design.
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